Perfluorochemical liquids because of their chemical inertness and because of the high solubility of oxygen and carbon dioxide in them offer promise for breathing liquids and artificial blood. For artificial blood or perfusion media they must be used in the form of emulsions. The perfluorodecalin family offers the most promise because these leave the body rapidly while many others remain in the liver for the lifetime of the animal. We are in the process of purifying certain of the commercial liquids and in synthesizing others. They are tested by intravenous infusion in animals.